Polycarbonate resin molded articles have been widely used as, for example, industrial transparent materials in the fields of electricity and electronics, machinery, automobiles, and the like or optical materials for lenses, optical disks, and the like because each of the articles is excellent in transparency and mechanical strength. When an additionally high mechanical strength is needed, a glass filler or the like is added to each of the articles to strengthen the article.
Glass fibers each constituted of glass generally called an E glass have been used as the glass filler. However, the refractive index of the E glass at a sodium D line (nD, hereinafter simply referred to as “refractive index”) is somewhat small, specifically, about 1.555, though, the refractive index of a polycarbonate resin is 1.580 to 1.590. Accordingly, when the glass filler is added to a polycarbonate resin composition in an amount needed for an increase in mechanical strength of the composition, the following problem arises: the resultant E glass-reinforced polycarbonate resin composition cannot maintain its transparency owing to a difference in refractive index between the filler and the polycarbonate resin of which the composition is formed, with the result that the composition becomes opaque.
Although a large number of patents each concerning a resin composition having a metallic external appearance or galactic external appearance (glittering pattern like the night sky studded with stars) have been filed, each of these patents discloses a resin composition using a transparent resin, and none of the patents describes a glass filler-reinforced resin. This is because of the following reason: when the resin to which glossy particles are added in order that a metallic external appearance or galactic external appearance may be obtained is not the transparent resin, only the glossy particles near the surface of a molded article are seen, so neither a metallic external appearance nor a galactic external appearance can be obtained.
To solve such problem, investigation has been conducted on, for example, a reduction in refractive index of a polycarbonate resin by the improvement of the resin or an increase in refractive index of a glass filler by the improvement of the composition of the glass filler.
For example, (1) a composition containing a polycarbonate resin composition using a product of a reaction between a hydroxyaralkyl alcohol and lactone as a terminal stopper and a glass filler having a refractive index smaller or larger than that of the polycarbonate resin composition by 0.01 or less (see Patent Document 1), (2) a composition composed of a polycarbonate resin, a glass filler having a refractive index smaller or larger than that of the polycarbonate resin by 0.015 or less, and polycaprolactone (see Patent Document 2), (3) a glass composition obtained by incorporating, for example, ZrO2, TiO2, BaO, and ZnO into a glass filler composition at a specific ratio so that the refractive index of the composition is close to that of a polycarbonate resin (see Patent Document 3), and (4) a glass filler-reinforced polycarbonate resin composition having a metallic external appearance (see Patent Document 4) have been proposed.
However, the polycarbonate resin composition in the above section (1) is not practical because of the following reasons: when the glass filler is added in an amount needed for an increase in mechanical strength of the composition, the difference in refractive index at such level is not small enough for the addition to exert its effect, and the glass filler is too expensive to be used as a raw material for the production of the polycarbonate resin composition.
The polycarbonate resin composition in the above section (2) involves the following problem: reductions in heat resistance and mechanical properties of the composition are inevitable owing to the presence of polycaprolactone, though, the composition can maintain its transparency even when the glass filler has a refractive index smaller or larger than that of the polycarbonate resin by 0.015 or less.
Unless the content of each of, for example, ZrO2, TiO2, BaO, and ZnO in the glass composition in the above section (3) is appropriately adjusted, the glass filler composition will devitrify. As a result, even when the glass filler composition has a refractive index equal to that of the polycarbonate resin, a polycarbonate resin composition containing the glass filler composition may be unable to obtain transparency. In addition, the significance of the use of a glass filler-reinforced polycarbonate resin composition for the purpose of a weight reduction wanes because the specific gravity of the glass filler itself increases.
Further, the document disclosing the polycarbonate resin composition in the above section (4) does not refer to flame retardancy. Accordingly, unless flame retardancy is imparted to the composition, fields where the composition can be used will be limited.
Patent Document 1: JP H07-118514 A
Patent Document 2: JP H09-165506 A
Patent Document 3: JP H05-155638 A
Patent Document 4: JP H06-212068 A